Turbine engine

ABSTRACT

A turbine engine, particularly for aircrafts, of the type comprising a rotor and at least two stages of stator blade rows positioned upstream and downstream of the rotor, wherein the rotor blades ( 8 ) are of the variable pitch type and have a drop shape, are of the twisted type ( 1 ) or of the constant deflection type ( 2 ) and the stator blades ( 25 ), positioned downstream of the rotor, are of the twisted type.

[0001] This invention refers to a turbine engine with variable pitchrotor blades having a drop shape; the engine according to the inventioncan advantageously also incorporate a “twisted” or a “constantdeflection” stator blade row in the Air-Intake and, in the nozzle, astator blade row with a movable twisted part.

[0002] This propulsion system, wherein the movable parts are controlledand actuated electrically, can be employed both for the aeronauticpropulsion and for the marine propulsion. Currently, the turbine enginesutilised in propulsion are predominantly of the Turbo-Engine type; as itis known, in this type of engines a turbine/compressor group rotates apower shaft to which a fixed pitch propeller located at the end of adivergent duct is connected; this duct called Air-Intake, usually freeof stator blades, has the scope to decelerate the air processed by therotor in order to increase the efficiency.

[0003] This propulsion systems have the same limits of the fixed pitchpropeller, which can be summarized as follows:

[0004] 1. the efficiencies decrease very rapidly above defined speeds Vof advancement;

[0005] 2. the resultant of the applied forces coincides at the end ofthe blades, with consequent bending stresses which alter the systemaerodynamics.

[0006] In the Engines with ducted propellers, which have the scope togenerate a thrust useful for the propulsion, none of the expedientswhich are proposed and justified in this analysis has been utilised.

[0007] In some jet engines, stator blade row (in some cases with movabletwisted part) are located upstream of the rotor in the stages of theaxial compressors, but to vary the performance modifying the pressureand to avoid the stall.

[0008] The variable pitch technique is instead widely utilised but onlyin the outside propellers for reasons that will be discussedhereinafter.

[0009] The turbine engine, with the drop shaped, variable pitch rotorblades, that is the object of this application, as claimed in claim 1,is proposed as a device capable to supply more efficiency than any otherpropulsion system of similar conception.

[0010] We will now describe the engine according to the invention, withreference to the attached drawings, in which:

[0011] FIGS. from 1 to 8 are mathematical vectorial models;

[0012]FIG. 9 shows a twisted stator blade from the a), b), c) and d)views which are the plan, front, side and perspective views,respectively;

[0013]FIG. 10 shows a constant deflection stator blade from the a), b),c) and d) views which are the plan, front, side and perspective views,respectively;

[0014]FIG. 11 is an exploded, perspective view of the propeller cuffwith the twisted stator blade;

[0015]FIGS. 12a, 12 b and 13 a are the exploded, assembled and sectionalviews of a rotor with variable pitch blades according to the invention;

[0016]FIG. 13b is a view of the variable pitch blade according to theinvention;

[0017]FIGS. 14a and 14 b are partially assembled and exploded views,respectively, of the stator part downstream of the rotor;

[0018]FIGS. 15a and 15 b are partially assembled and exploded views,respectively, of the engine casing downstream of the rotor;

[0019]FIG. 16 is the axial sectional view of the stator part and of theengine casing downstream of the rotor;

[0020]FIGS. 17a and 17 b are assembled and exploded views, respectively,of the stator part downstream of the rotor;

[0021]FIGS. 18, 19, 20 and 21 are efficiency diagrams;

[0022]FIGS. 22 and 23 are axial sectional views of the full engineaccording to the invention.

[0023] Now, we will see in details how we arrived to the invention andwhich are the concrete advantages in relation to the known art. To doso, we start from the mathematical models known in this sector.

[0024] The field diagram is a vectorial diagram where all the speedtriangles of each station can be represented, simultaneously, in aworking condition; for simplicity, in the enclosed figures, only thetriangles related to the stations on the hub (indicated by “m”) and atthe end (indicated by “e”) are represented.

[0025] The main scope of this diagram is to define with ease thedimensions of the twist of the propeller, either ducted or unducted; thetwist angles θ of the various airfoils, are the angles subtended by thevectors that represent the driving speed U and the relative speed W,defined, in the propeller wing theory, with the symbol β (appropriatelycalculated in the design phase as we can suppose from FIG. 1).

[0026] The values of the advancement speed V and of the driving speed Uare reported in this diagram, by changing them from m/sec to cm.

[0027] The reference to build this diagram is the rotation axis of thepropeller indicated in the figure with the initials A.r.. The drivingspeed U vectors are perpendicular to A.r., they are opposite to thepropeller rotation vector (we consider, for the reciprocity principle,the blade in a steady state and the air flowing on it), proportional tothe station taken in consideration and dependent from the number of therotor revolutions.

[0028] The advancement speed vector V depends instead from the type ofthe studied propeller:

[0029] for outside propellers and for ducted propellers, without statorstages upstream of the rotor, it is always parallel to A.r.;

[0030] for ducted propellers, supplied with stator blading located inthe Air-Intake, it is deviated by λ degrees and depends from the statortype (twisted or with constant deflection).

[0031] In FIG. 2 a field diagram is represented which gives the schemeof the presence of a stator twisted blading (to be noted how, at thehub, V is deviated of λ_(m) degrees with respect to A. r., while at theend it is parallel).

[0032] In FIG. 3 a field diagram is represented which gives the schemeof the presence of a stator twisted blading which deviates the flowlines, at each station, of λ degrees.

[0033] As shown in FIG. 4, in a duct, positioned downstream of thestator blade row which deviate the direction of the flow lines of λdegrees, the speed vector V′ is the vectorial sum of the axial speed Vand of a component τ which is generated perpendicularly; in fact theaxial speed V of the particles contained in a constant section duct cannot change otherwise the flow rate would change.

[0034] Let's clarify the base theory on which the Engine, according tothe invention, is based by introducing the concepts of efficacy E and ofefficiency η of the propeller and by linking said concepts to the fielddiagram.

[0035] The propulsion efficacy E is defined as the ratio between thedriving force T developed by the propeller and the resisting force F_(r)which resists to the propeller rotation. T and F_(r) are respectivelythe forces which act along the parallel and the perpendicular directionto the rotation axis of the rotor; they are equal, in module, to thealgebraic sum of the vectorial components of the Lift L and of the DragD along said directions.

[0036] With reference to FIG. 5, we can then write the followingrelations valid in each section of the blade:

T=Lcosβ−Dsinβ=½ρSW ²(C ₁Cosβ−C _(d)Sinβ)

F _(r) =Dcosβ+Lsinβ=½ρSW ²(C _(d)Cosβ+C ₁Sinβ)

[0037] where ρ is the density, S is the area, W is the relative speedand C₁ and C_(d) are the lift and drag coefficients, respectively.

[0038] By indicating explicitly the terms from which the propulsionefficiency depends and through appropriate passages we have:$E = {\frac{T}{Fr} = \frac{\left( {C_{1}/C_{d}} \right) - {{Tg}\quad \beta}}{{\left( {C_{1}/C_{d}} \right){Tg}\quad \beta} + 1}}$

[0039] As it can be seen from this last relation, the lower the value ofβ and the higher the efficiency value.

[0040] The efficiency η instead is defined as the ratio between the workyield and the work spent:

η=L _(yield) /L _(spent) =TV/Cω

[0041] Where T is the Propeller driving force, V is the advancementspeed, C is the torque needed by the rotatory movement and ω is theangular speed.

[0042] Knowing that, at each reference station, the value of the torqueneeded to rotate the blade is the product between the drag force and thedistance from the rotation axis R, on which Fr acts (the total torque isthe sum extended to the all area of the blade C=ΣF,R) and by recallingthat U=ωR, the formula of the efficiency η becomes:$\eta = {\frac{TV}{C\quad \omega} = {\frac{TV}{\sum\limits^{\quad}\quad {F_{r}R\quad \omega}} = {\frac{TV}{\sum\limits^{\quad}\quad {F_{r}U}}\alpha \quad E\frac{V}{U}}}}$

[0043] As it can be seen, η is proportional to the efficacy E and shouldincrease in relation to the increase of the speed V because U is limitedby the maximum number of revolutions: in reality the efficiencyincreases until a certain value of V, but then it starts to decreasebecause the increase of V increases the angles β which cause the valueof the efficacy to decrease more than the increase of the ratio V/U.

[0044] The values of η are generally referred to the ratio ofadvancement γ (proportional to the ratio between the advancement speed Vand the number of revolutions n) and typically have the path shown inFIG. 6.

[0045] The base idea, at this point, is to increase the efficiency byintroducing stator blades in the Air-Intake to reduce the value of β.

[0046] By analysing the field diagram of a traditional Engine, shown inFIG. 1, it can be seen how β_(m) is larger than β_(e); we then rotatethe advancement speed V vector, at the hub station, by λ_(m) degrees sothat the vector W_(m) becomes parallel to W_(e) (FIG. 2). The sameprocedure is repeated (but not shown) for all the sections taken as areference.

[0047] We have introduced in this way a twisted stator that, in thedesign conditions of the stator twist, cause, in all the sections, theangles β equal to the value present at the end of the blade, where ithas been demonstrated that there is the highest efficiency. FIG. 2represents the design technique of the stator twist: in the designcondition (identified by the ratio of advancement Υ_(ps)) the statorairfoils must deviate the advancement speed V so as to generate relativespeed vector W always equal, in module and in direction, in all thesections.

[0048] Supposing that FIG. 7a identifies the design condition of thestator twist (identified by the advancement ratio Υ_(ps)) and knowingthat the angles λ stay constant for all the situations, we can noticethat, in the Engine according to the invention, with values of Υ lowerthan Υ_(ps) (FIG. 7/b) the angles β are a little bit larger close to thehub; on the contrary, with values of γ higher than γ_(ps) (FIG. 7/c) theangles β are even smaller. It is clear then that the total efficiency ishigher in the version proposed at the beginning, since, with the sameworking conditions, the values of β are smaller in the Engine accordingto the invention, if compared with the values of the modern propulsionsystems.

[0049] In the version of the Engine according to the invention withconstant deflection stator blading (FIG. 3), the value of the angles β,in all the sections of the blade, have also a value lower than thevalues of the Engine and of the Propeller blades; it is clear that, alsoin this version, the efficiency is optimised.

[0050] In the Engine according to the invention, with twisted statorblading, blades having the surface concentrated towards the hub areused, primarily for two reasons which can be understood from FIG. 7:

[0051] the value of the aerodynamic forces is directly proportional tothe square of the relative speeds W which have a value, in module,always higher towards the hub with respect to the Engine (even withvalues higher than γ_(ps), the modules of the vectors W at the hub arehigher than the vectors at the end of the blade).

[0052] with values of the advancement ratio higher than γ_(ps), (cruiseconditions) the airfoils at the hub work with efficiencies higher thanat the end (β_(m) lower than β_(e)).

[0053] Therefore, in the Engine according to the invention with thetwisted stator blading, besides an increase in the efficiency, theresultant of the aerodynamic forces generated by the blades is appliedcloser to the hub and the value of the centrifugal force relative to theblades has a lower value since the mass is concentrated closer to thecentre of rotation; consequently, the structural stresses are lower.

[0054] Further, in the Engine according to the invention with thetwisted stator blading, the chords of the blade can be dimensioned so asto obtain (at least in a certain condition) an elliptic distribution ofthe lift that, according to the Aerodynamic Theory, generates a value ofproduced Drag lower than any other type of distribution.

[0055] Going to conclude the description of the stator blading locatedin the Air-Intake, we call the attention to FIGS. 9, 10 e 11 which show,respectively:

[0056] the Engine version according to the invention, with the twistedblade 1 in the plan (a), front (b), side (c) and perspective d) views;

[0057] the Engine version according to the invention with the constantdeflection blade 2 shown in the same views of the twisted blade in thepreceding figure;

[0058] the assembly of the blades according to the invention in the AirIntake 4 and in the propeller cuff 3 which can be split in two pieces;the scope of the hole 5 in the blade 1 a is to form a passage forelectric wires of the slip-rings.

[0059] The use of the variable pitch propeller in the engine accordingto the invention is motivated by the benefits that can be obtained andthat are described here below:

[0060] 1. A variable pitch propeller, under all circumstances, can bepositioned in the best conditions with respect to the field ofinstantaneous speed ε (angle comprised between the relative speedvectors W_(e) and W_(m), shown in FIGS. 1, 3 and 8 b) so as that allairfoils always work at the maximum efficiency;

[0061] a variable pitch propeller can obtain advancement speed V higherthan the fixed pitch propellers (in fact if a fixed pitch propeller isdimensioned for high speeds V, the stagger angle would be so high thatwith low values of V the airfoils would go in stall conditions; on thecontrary, in the variable pitch propeller, even if the twist of theblade is dimensioned for high values of V, at low speeds, the blade canbe positioned so that all the sections work at incidence angles which donot cause the stall);

[0062] 3. a variable pitch propeller, at any time, can work as a brakeor as a thrust reverser (on the contrary a normal blade can work as abrake only when the angles β are higher than the airfoils staggerangles).

[0063] It is evident that the variable pitch propellers are widelyutilised in many aircrafts but they do not have yet find an applicationin the Fan.

[0064] The proposed variable pitch system, which is activated by anelectric motor, is of the screw/female thread type and is contained inthe rotor represented by FIGS. 12a, 12 b, and 13 a in an exploded,assembled and sectional view, respectively.

[0065] The rotor is formed by four parts 6 a, 6 b, 6 c and 6 d whichcontain, in circular housings 7 (FIG. 12a), obtained in the transversesections having a polygonal section, the blades 8; in the part 6 c,helicoidal cavities 9 (FIG. 12b) are obtained in order to balance thegeometry change, from the circular to the polygonal shape, by directingthe fluid toward the blades with the maximum efficiency.

[0066] The motor 10 is directly connected to a planetary gearbox 11 andto an encoder 12 and is powered by a slip-rings (not shown) linked closeto the front bearing. The reduction gear shaft 11 is linked to a wormscrew (formed by the parts 12 and 13) on which a threaded ring nut 14moves by rotation; the bushes 16 (connected to the eccentric arms 18 ofthe plate 19 by means of elastic rings 17) are retained in the groove 15obtained in the ring nut 14. When the ring nut 14 moves axially, theplate 19 causes the blade 8 to rotate, transferring the rotation fromthe cavities 20 to the slots 21 (see FIG. 13b).

[0067] The axial loads transferred from the ring nut 14 to the screw (12and 13) are unloaded on the rotor parts 8 b and 8 c through axial rollerbearings 22 (FIG. 12a). The centrifugal force due to the blade 8 and tothe related components is instead unloaded on the rotor parts 6 c and 6d through the axial roller bearings 23 (FIG. 13b). The drop shaped blade8, comprised in the rotor 6, is also represented in FIG. 8a (in a sideand in a sectional view); the typical shape of the blade plan isobtained by locating some of the pressure centres of the airfoils Cp(points on which the resultants of the aerodynamic forces are applied)upstream and others downstream of the variable pitch rotation axis x, sothat the torques, which are generated because of the aerodynamic forces,balance each other, thus allowing the use of a low power input toactivate the variable pitch. The airfoils on the hub and at the end arepositioned so that the axis x coincides with the centre line of thechord; while the other airfoils are positioned so that, under allcircumstances, the resulting torque change within a minimum value range;therefore the line that joins the Cp of all the blade airfoils, has thetypical sinusoidal path shown in the side view of the blade of FIG. 8a.

[0068] The bottom of the blade is circular and it is housed in thecircular cavities 7 obtained in the rotor parts 6 c and 6 d; in this waythe formation of the Von Karman vortices, which would reduce theefficiency, is avoided, see FIG. 12.

[0069] We have discussed the twist technique of the stator blades 1 withthe help of the field diagram; then, we will show, as an example, how todetermine the twist of the blades 8.

[0070] Known the values of the stator defection λ, obtained under theconditions of the advancement ratio γ_(ps), we have first of all todecide the value of the design advancement ratio of the rotor twist(γ_(pr)). From FIG. 7, it is clear that, in order to obtain positiveincidence angles in all the sections, γ_(pr) must be lower than γ_(ps);the optimal value will depend from the outer diameter of the blades andfrom the advancement speed V that we intend to reach.

[0071] The twist condition is that, once defined the stator deflectionangles and the value of γ_(pr), the twist angles θ, in all the sectionsof the blade 8, coincide with the angles β; in this situation, as it isshown by the speed triangles, adjacent to the sections A-A, B-B, e C-Cof FIG. 8a (extrapolated from the field diagram of FIG. 8b), the airfoilchords are parallel to the relative speed vectors. The function of thestators downstream of the rotor is to eliminate the swirl of the fluidflow rate processed by the rotor in order to increase the pressure andtherefore the thrust.

[0072] The movable twisted part, in the stator blade row downstream ofthe rotor, is necessary to reduce to a minimum the pressure losses andthe structure stresses; in fact the speed range ε out from the rotor isnot constant during time but it changes both in amplitude and inorientation, with respect to the reference system common to bothconditions.

[0073] This means that, by dimensioning the twist of the movable part,under proper design conditions, and by controlling the position of thesurfaces (so that the airfoil chords form incidence angle values whichare almost zero), we obtain, on said surfaces, reduced energydissipation and undesired aerodynamic forces in comparison with the casewhere fixed surfaces would be used.

[0074] The exploded and assembled view of such device are represented inFIGS. 14 e 15; the side sectional view is instead shown in FIG. 16.

[0075] The movable parts of the stators are driven by the electric motor24; the blades 25 have, at their free ends, projecting folded levers 26,whose axis x is rigidly connected to the rotation centre of the blades25. The projecting ends of the levers 26 are housed in eyelets obtainedin the ring gear 28; said ring is linked to the outer structure 4 of theengine by means of the shoulders 29 and of the pins 30 obtained on theouter structure (See FIG. 15b).

[0076] When the motor 24 rotates, by means of a coupling with conicgears (28 and 31), also the ring 28 rotates and, by dragging the levers26, causes the blades 25 to rotate.

[0077] The actuation and the control of the movable surfaces is done byelectric means, because this type of technology allows a better workingflexibility and a better precision on the positioning: an electroniccentral unit processes, as input data, the advancement speed and thenumber of revolutions of the propeller and, thanks to the software withwhich the central unit is programmed, it drives the two electric motorswhich move the rotor pitch mechanisms and the pitch mechanisms of themovable stator part, respectively.

[0078] The positions of the blades 8 and 25 are respectively activatedthrough the feedback by the encoders 12 (FIG. 13a) and 32 (FIG. 16)which send to the central processing unit a comparison electric signalwhich is proportional to the instantaneous position.

[0079] The rotor is set in rotation by a conic couple of gears,contained in the gear oil sump 33, by means of a power shaft 34contained inside the stator blades downstream of the rotor (see FIG.17). The rotor is linked to the gear oil sump 33 and to the propellercuff 3 by means of ball or roller angular bearings mounted with a “O”disposition.

[0080] The control of the propeller pitch is different from that of themovable part of the stator because there is the possibility to position,through a control in the cockpit, the blade at an offset angle withrespect to the position controlled by the central unit, this controlallows the pilot to manage directly the performances of the propulsionsystem. This control procedure is valid within the stall limits.

[0081] We conclude the theory description of the innovations introducedin the Engine according to the invention, by showing the diagrams of theefficiency represented in FIGS. 18, 19, 20 e 21 which refer to a fixedpitch Fan, to a variable pitch Fan, to a variable pitch Fan according tothe invention with constant deflection stator blades and to a variablepitch Fan according to the invention with twisted stator blades,respectively.

[0082] The diagrams clearly summarize the advantages that the proposedand explained innovations make happen in the Engine according to theinvention with respect to the current art of the Fan available on themarket.

[0083] Finally, FIGS. 22 and 23 show the engine according to theinvention (dimensioned and complete with all the needed parts).

1. A turbine engine, particularly for aircrafts, of the type comprisinga rotor and at least two stages of stator blades positioned upstream anddownstream said rotor, characterized in that the rotor blades (8) are ofthe variable pitch type and have a drop shape.
 2. A turbine engineaccording to claim 1, characterized in that the stator blades (1),positioned before the rotor, are of the twisted type.
 3. A turbineengine according to claim 1, characterized in that the stator blades(2), positioned before the rotor, are of the constant deflection type.4. A turbine engine according to claim 1, characterized in that thestator blades (25), positioned after the rotor, are of the twisted type.5. A turbine engine according to claim 1, characterized in that thevariable pitch of the rotor blades (8) is activated by an electric motor(10) which controls a screw female thread system contained in the rotor;said rotor is formed by four parts (6 a, 6 b, 6 c and 6 d) whichcontain, in circular housings (7) obtained in the transverse sectionswith polygonal section, the blades (8); in one of the four parts (6 c),helicoidal cavities (9) are obtained which balance the geometry change,from the circular to the polygonal shape, by directing the fluid towardthe blades.
 6. A turbine engine according to claim 5, characterized inthat the motor (10) is directly connected to a planetary gearbox (11)and to an encoder (12) and is powered by a slip-rings; the reductiongear shaft (11) is linked to a worm screw on which a threaded ring nut(14) moves by rotation; the bushes (16), connected to the eccentric arms(18) of the plate (19) by means of elastic rings (17), are retained inthe groove (15) obtained in the ring nut (14).
 7. A turbine engineaccording to claim 1, characterized in that the rotor is set in rotationby a conic couple of gears, contained in a gear oil sump (33), by meansof a power shaft (34) contained inside the stator blades which arepositioned downstream of the rotor; said rotor is linked to the gear oilsump (33) and to the propeller cuff (3) by means of ball or rollerangular bearings mounted with a “O” disposition.
 8. A turbine engineaccording to claim 1, characterized in that the typical drop shape ofthe blade plan, contained in the rotor (6), is obtained by locating someof the pressure centres of the airfoils Cp upstream and other pressurecentres downstream of the variable pitch rotation axis (x), so that thetorques, which are generated because of the aerodynamic forces, balanceeach other, thus allowing the use of a low power input to activate thevariable pitch; the airfoils on the hub and at the end are disposed soas that the axis (x) coincides with the centre line of the chord, whilethe other airfoils are disposed so as that, under all circumstances, theresulting torque change within a minimum value range, therefore the linethat joins the (Cp) of all the blade airfoils, has a sinusoidal path(y).
 9. A turbine engine according to claim 2, characterized in that, inthe design phase, the stator airfoils must deviate the advancement speedV so as to generate relative speed vector W always equal, in module andin direction, in all the sections to the vector W_(e) closed at the endof the blade; thus in the velocity triangles, of all the rotor bladessections, angles (β) are equal in value to the angles at the end of theblade, where it has been demonstrated that there is the highestefficiency.
 10. A turbine engine according to claim 4, characterized inthat the stator blades positioned downstream of the rotor are formed bya fixed part and by a movable part (25).
 11. A turbine engine accordingto claims 4 and 10, characterized in that the movable part (25) of thestator blades positioned downstream of the rotor are driven by anelectric motor (24); the blades (25) have, at their free ends,projecting folded levers (26), whose axis x is rigidly connected to therotation centre of the blades (25); the projecting ends of the levers(26) are housed in eyelets (27) obtained in the ring gear (28); saidring is linked to the outer structure (4) of the engine by means of theshoulders (29) and of the pins (30) obtained on the outer structure; byactivating the motor (24), by means of the coupling with conic gears (28and 31), also the ring (28) rotates and, by dragging the levers (26),causes the blades (25) to rotate.
 12. A turbine engine according to theprevious claims, characterized in that the actuation and the control ofthe blades 8 and 25 are of the electric type; an electronic central unitprocesses, as input data, the advancement speed and the number ofrevolutions of the propeller and, thanks to the software with which thecentral unit is programmed, it drives the two electric motors which movethe rotor pitch mechanisms and the pitch mechanisms of the movablestator part, respectively; the positions of the blades 8 and 25 arerespectively activated through the feedback by the encoders 12 and 32which send to the central processing unit a comparison electric signalwhich is proportional to the instantaneous position.
 13. A turbineengine according to the previous claims, characterized in that thecontrol of the propeller pitch is different from the control of thepitch of the stator movable part because there is the possibility toposition the blade at an offset angle with respect to the positioncontrolled by the central unit.